This invention relates generally to electric switch assemblies and, more particularly, to electric switch assemblies having a magnetic reed switch.
Switch assemblies having magnetic reed switches are used for a variety of applications and are especially popular for use with devices that require hermetically sealed housings. A typical switch assembly in a sealed device includes a trigger with an attached magnet, which move together relative to a housing, and also includes a magnetic reed switch that remains stationary inside the housing. When the trigger is moved relatively closer to the housing into a closed position, the trigger magnet is moved closer to the reed switch and induces a magnetic field around the reed switch that is sufficiently strong to close it. When the trigger is moved away from the reed switch into an open position, the trigger magnet is moved away from the reed switch. This reduces the magnetic field around the reed switch sufficiently to open it. Thus, the difference in the magnetic field around the magnetic reed switch between the open and closed positions of the trigger is used to operate the switch.
Because the trigger magnet produces lines of magnetic force that can penetrate relatively thin materials, such as plastic, the magnetic reed switch can be placed inside the device's sealed housing and the trigger magnet still can be moved sufficiently close to the switch to open and close it. A hermetically-sealed housing provides a much better barrier against the entry of dirt and moisture around the electrical switch assembly and into the housing when compared with conventional mechanical contact switches. Moreover, magnetic reed switches have much greater reliability and normally can operate throughout the life of the device without requiring maintenance or replacement, which would necessitate opening the sealed housing. Thus, magnetic reed switches of this type are especially popular for devices where it is important to maintain hermetically-sealed housings. One such device is a laser bar code scanner.
Laser bar code scanners include a low-power laser that emits a beam and further include scanning means for directing the beam at an adjacent bar code data pattern having alternating light and dark stripes of varying width, representative of alphanumeric data. More of the beam is reflected from the light stripes than from the dark stripes and therefore the reflected beam is indicative of the bar code pattern. The scanner receives the reflected light and detects the bar code pattern, after which it quickly and accurately deciphers the reflected beam into the correct alphanumeric data. Portable laser scanners are widely used to track the level of inventory and the location of packages that are marked with bar code data, among other uses. It is very important for such scanners to be easily operable, with great reliability, under a wide variety of environmental conditions. Thus, such scanners often have a sealed housing and use a magnetic reed switch to operate the laser.
Magnetic reed switches of the kind used in laser bar code scanners must be manufactured within stringent tolerances. For example, the associated trigger is typically pivoted through a relatively small range of movement, such as an arc of only 10.degree., to open and close the magnetic reed switch. As a result, the reed switch must be precisely positioned within the housing relative to the trigger and the magnet so that movement of the trigger will provide sufficient disparity in the strength of the magnetic field to consistently open and close the reed switch. Even with precise reed switch placement, devices incorporating magnetic reed switches often must be individually adjusted at the point of manufacture to ensure consistent switching operation. These requirements greatly increase the cost of manufacturing such devices.
Although the electric switch assembly of the laser bar code scanner described above has proven to be generally satisfactory, it is believed that the electric switch assembly can be improved upon in several respects. For example, if the reed switch of the electrical switch assembly did not need to be precisely placed within the housing and did not need to be individually adjusted, the cost of manufacturing products requiring a hermetically sealed housing could be reduced.
It will thus be appreciated from the foregoing that there is a need for an electric switch assembly that does not require precise placement and adjustment of a reed switch during manufacturing and that will perform consistently throughout the life of the associated device. The present invention satisfies this need.